Blender weight paint, brush doesn't work properly on the mesh it barely affects the object
I tried to duplicate your video to no similar results, but It looks like is had to do with some setting you must have changed. On the left hand side check the dropdown menu for stroke and curve and check those settings, Stroke should be on space, and curve should look like its going top left to bottom right in a slope. If that doesnt work check the options tab on the left and make sure restrict is not checked on and neither is the x mirror or topology mirror.

If all else fails, under the file tab all the way up top just select "load factory settings" and that should resolve your issue. And if that fails then maybe it was a bug in the version you're using which is very old, you should update to the latest stable build which is 2.79